Field of the Invention
The invention relates to monophosphites having an unsymmetric biaryl unit and their utility as ligands in hydroformylation.
The biaryl units of the invention have, for example, a phenyl-phenyl unit or a naphthyl-phenyl unit.
Discussion of the Background
The reactions between an olefin compound, carbon monoxide and hydrogen in the presence of a catalyst to give an aldehyde comprising one additional carbon atom are known as hydroformylation or oxo synthesis. In these reactions, compounds of the transition metals of group VIII of the periodic table of the elements are frequently employed as catalysts.
Known ligands include, compounds of the phosphine, phosphite and phosphonite classes each comprising trivalent phosphorus PIII. A good overview of the state of the hydroformylation of olefins can be found in B. CORNILS, W. A. HERRMANN, “Applied Homogeneous Catalysis with Organometallic Compounds”, vol. 1 & 2, VCH, Weinheim, New York, 1996 or R. Franke, D. Selent, A. Börner, “Applied Hydroformylation”, Chem. Rev., 2012, DOI:10.1021/cr3001803.
The disadvantage of bi- and polydentate phosphine ligands is a relatively high level of complexity necessary for preparation thereof. It is therefore often unviable to use such systems in industrial processes. An additional factor is comparatively low activity, which has to be compensated for by chemical engineering, through high residence times. This in turn leads to unwanted side reactions of the products.
In Angew. Chem. Int. Ed. 2000, 39, No. 9, p. 1639-1641, Börner et al. describe ligands having one P—C bond and two P—O bonds; these are thus phosphonites. The phosphonites described therein, when used in hydroformylation, have n/iso selectivities (n/iso=the ratio of linear aldehyde (=n) to branched (=iso) aldehyde)) of 0.61 to 1.57.
The phosphonite ligands described in DE 199 54 721 have a good n/iso selectivity. However, in-house studies have shown that the compound II-c (in DE 199 54 721; page 6) has a tendency to photochemically induced breakdown, and should therefore not be used on the industrial scale.
One disadvantage of the ligands having a phosphonite structure is that their preparation is very complex. The possibility of a favourable and simple synthesis is crucial for the use of ligands in an industrial scale process.
The ease of availability and the associated likelihood of industrial scale use is an important criterion, since the preparation complexity and the associated costs that arise may only be so high if the viability of the overall process is to be obtained.
Rhodium-monophosphite complexes in catalytically active compositions are suitable for the hydroformylation of branched olefins having internal double bonds.
Since the 1970s, there have been descriptions of the use of “bulky phosphites” in hydroformylation (see, inter alia, van Leeuwen et al., Journal of Catalysis, 2013, 298, 198-205). These feature good activity, but the n/iso selectivity for terminally hydroformylated compounds is low and in need of improvement.
EP 0 155 508 discloses the use of bisarylene-substituted monophosphites in the rhodium-catalysed hydroformylation of sterically hindered olefins, e.g. isobutene. Rhodium concentrations used here are sometimes very high (one being 250 ppm), which is unacceptable for an industrial scale process in view of the current cost of rhodium and has to be improved.
Even though a multitude of ligands and the use thereof in rhodium-catalysed hydroformylation are known, it is desirable to develop new ligands having improved properties.